Return air Plenum - failed inspection
sorry in advance for the long post, but i need some advice I am building an addition on my house here in FL. I have done the HVAC myself and today i failed inspection. here is what iv built. the return plenum box is built from a single piece of 1 1/2 duct board, sealed at all joints with metal backed tape and covered with mastic. I cut sheet metal found in the air duct section at home depot into 4x22 strips. I put a layer of mastic around the face of the opening , then applied the strips of metal to the edges of the opening, taping the ends to the box, and to the other metal strips, this formed a metal frame around the opening of the plenum box. i thought a pic of what i have might help? here is the failure verbose from the inspection notice. code: FEC 1601.3.2 --- I assuming the FEC refers to Florida Energy code i cant even find this code either in the mechanical section of the building code book, or in chapter 13, the energy efficiency section. Return Plenum will need can stock properly installed per the fl. Energy Code - the metal installed is not can stock what is can stock? and how is this different from the metal strips I cut and installed? I haven't seen it called can stock, but the way you have that built should fail just about any mechanical inspection. Here is a really bad picture I drew in windows paint of a cross section detail of how the connection is supposed to be done to the unit, assuming this is a horizontal installation. If it isn't a horizontal installation, ductboard isn't a wise material choice to begin with. Tape or mastic the joint The foil tape visible in your picture is crap, metal foil tape is much better. The stuff shown will delaminate and release from the ductboard over time. Its actual rated use is only for ductboard to ductboard connections, and it is to be stapled down. Even when it is used correctly, it is still crap though. What size system is it? That return duct looks like it may be horribly under sized for any capacity system that would have the physical size air handler that plenum would fit.... It also looks like you have a lot of compression of the inner liner of the duct, like it wasn't fully stretched out. big performance killer. Got more pictures of the duct system. I also am lost here on what he wants. Like Marks lay out have did it that way many times. Have also bent up like a 4 deep U and screw the bottom of the U on to the blower unit. Slide the ductboard in it . And some screws and mastic to hold the duct in it. I just spent 25 years down there in west palm and i sure dont get what he wants. Might read this chapter #6 For there. But I know every little town there has its own code http://www.iccsafe.org/cs/codes/pdf/...Mechanical.pdf First i will address the tape since that is not the first time i have heard this is junk. I bought all my supply from General insulation here in Orlando, they told me this was the BEST tape and UL181? (i think that was the number) rated... I knew i should have gone with the stuff from homedepot with the red lettering on it... ok back to the duct.. thank you very much for the drawing, I think from the drawing, that i have explained this connection wrong , my picture is not showing the connection of the return air duct to the air handler.. What i am picturing here is actually the wall return in the master suit where the intake grill will later be fastened to the wall, this location is about 12ft up the wall in a hallway leading to the master bedroom. so this has nothing to do with the handler , it is just a boot? to connect the intake grill to the return line... the system size will be 3 1/3 tons per the prints. The duct is actually 14 ,and this is only have of the return system, the other half is existing in the other side of the house, the duct may looked compress because the angle of the picture combing with the fact that the duct also is angled away from the box to get into the attic from where the box sits. here is a shot from bellow the intake boot? looking up from the hallway sure i have more pics! let me know if you need any other shots to help me out here...once again i appreciate all you help! here is a pic looking down the hallway, just to show the orientation of this boot? box? the place where the return air grill will mount after the drywall is installed... here is my picture of the box, because the hole cutout on the box is slightly smaller that the box is self, it creates a lip, rather than bending the metal more than once, do you think that putting the screw in from the inside would be ok? and my last question is.. is the return grill is 18x18.. is that a rough size for the hole? as apposed to the finished size of the grill? so i assume the hole positions would be somewhere around 20-21 apart? thanks again! PS. if you guys ever need computer help ... let me know! (the engineer, in my domain name aaronengineering.com, comes from me being a computer engineer, not mechanical!) i sure appreciate the help !
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